Designing star-shaped subphthalocyanine-based acceptor materials with promising photovoltaic parameters for non-fullerene solar cells

Abstract

Star-shaped three-dimensional (3D) twisted configured acceptors are a type of nonfullerene acceptors (NFAs) which are getting considerable attention of chemists and physicists on account of their promising photovoltaic properties and manifestly promoted the rapid progress of organic solar cells (OSCs). This report describes the peripheral substitution of the recently reported highly efficient 3D star-shaped acceptor compound, STIC, containing a 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC) end-capped group and a subphthalocyanine (SubPc) core unit. The 3D star-shaped SubPc-based NFA compound STIC is peripherally substituted with well-known end-capped groups, and six new molecules (S1-S6) are quantum chemically designed and explored using density functional theory (DFT) and time-dependent DFT (TDDFT). Density of states (DOS) analysis, frontier molecular orbital (FMO) analysis, reorganization energies of electrons and holes, open-circuit voltage, transition density matrix (TDM) surface, photophysical characteristics, and charge-transfer analysis of selected molecules (S1-S6) are evaluated with the synthesized reference STIC. The designed molecules are found in the ambience of 2.52-2.27 eV with a reduction in energy gap of up to 0.19 eV compared to R values. The designed molecules S3-S6 showed a red shift in the absorption spectrum in the visible region and broader shift in the range of 605.21-669.38 nm (gas) and 624.34-698.77 (chloroform) than the R phase values of 596.73 nm (gas) and 616.92 nm (chloroform). The open-circuit voltages are found with the values larger than R values in S3-S6 (1.71-1.90 V) and comparable to R in the S1 and S2 molecules. Among all investigated molecules, S5 due to the combination of extended conjugation and electron-withdrawing capability of end-capped acceptor moiety A5 is proven as the best candidate owing to promising photovoltaic properties including the lowest band gap (2.27 eV), smallest λe = 0.00232 eV and λh = 0.00483 eV, highest λmax values of 669.38 nm (in gas) and 698.77 nm (in chloroform), and highest Voc = 1.90 V with respect to HOMOPTB7-Th-LUMOacceptor. Our results suggest that the selected molecules are fine acceptor materials and can be used as electron and/or hole transport materials with excellent photovoltaic properties for OSCs.